The present invention relates generally to optoelectronic and fiber optic components and, more particularly, to methods of joining optically coupled optoelectronic and fiber optic components.
Optoelectronic and fiber optic components (collectively referred to hereinafter as xe2x80x9coptoelectronic componentsxe2x80x9d) convert electrical signals to visible or infrared radiation and/or vice-versa and/or serve as a waveguide for visible or infrared radiation. Examples of optoelectronic components include optical fibers, light guides, fiber optic connectors, fiber arrays, dense wavelength division multiplexers (DWDM), arrayed wave guides (AWG), couplers, lenses, gratings, filters, tunable lasers, vertical cavity surface emitting lasers (VCSEL), transmitters, receivers, transceivers, switches, modulators, routers, cross-connects, optomechanical switches, electro-optical switches, wavelength converters, repeaters, regenerators, optical amplifiers, optical sensors, photocells, solar cells, optoisolators, LEDs (light-emitting diodes), laser diodes, etc. Optoelectronic devices play an increasingly important role in many areas including telecommunications, photovoltaic power supplies, monitoring and control circuits, computer storage, optical fiber communications, medical devices, etc.
It is generally considered critical that optoelectronic components be assembled with high precision to assure proper optical alignment (referred to as optical xe2x80x9ccouplingxe2x80x9d). In order to effectively couple optical signals between optical fibers and/or between optical fibers and other optical components, a fiber optic connector must maintain the precise alignment of the individual optical fibers in a predetermined manner such that the optical fibers will remain aligned as the fiber optic connector is mated with another fiber optic connector or with other types of optical devices. Conventional assembly techniques for joining optical fibers and/or components utilize a curable adhesive (e.g., epoxy) to attach optical fibers to a substrate.
The primary role of adhesives is to enable assembling complex shapes of similar or dissimilar materials. Of equal importance is the reliability of the joint/bond enabled by the adhesive chemistry. Adhesive selection is based on various criteria including the ability to provide a reliable joint over the life expectancy of the optoelectronic product and the ability to sustain environmental exposure during the operational life of the optoelectronic product. Some of the key adhesive properties guiding adhesive selection include: coefficient of thermal expansion, glass transition temperature, fracture toughness, modulus, moisture up-take, adhesive strength, cure shrinkage, viscosity and optical properties.
There are two main categories of adhesives used in optoelectronic packaging: reactive systems (referred to hereinafter as xe2x80x9cthermal cure adhesivesxe2x80x9d) and photo-polymerizing systems (referred to hereinafter as xe2x80x9cUV-curable adhesivesxe2x80x9d). Both types of adhesives require curing. Thermal cure adhesives require heat and UV-curable adhesives require a combination of ultraviolet (UV) radiation and heat. However, the properties of these two types of adhesives are different. Thermal cure adhesives are typically more stable post-cure than UV-curable adhesives and typically result in less moisture pick-up and better mechanical properties. Unfortunately, thermal cure adhesives may require a long cure time. In contrast, UV-curable adhesives cure much faster than thermal cure adhesives. Accordingly, UV-curable adhesives are often the preferred choice for rapid assembling of optoelectronic components. In operation, optoelectronic components are joined to create an assembly, an adhesive is applied to an interface between the components, and then the components are aligned and exposed to UV radiation to partially cure the adhesive prior to moving the assembly to a thermal cure station for completion of the cure.
A limitation of UV-curable adhesives is that line of sight is required for UV radiation to reach an adhesive to be cured in order to trigger the photo-initiators responsible for cure. Unfortunately, special design configurations of optoelectronic component assemblies may obstruct light paths, thereby creating a shadow at an interface. The shadowing effect may result in poor curing of the adhesive.
To align optoelectronic components being assembled, a light source (e.g., a laser) transmits light through the optoelectronic components being assembled and a photodetector measures the amount of light passing therethrough. The positions of the optoelectronic components are incrementally adjusted relative to each other (typically via mechanical nano-positioner devices) until the light transmitted therethrough reaches a maximum (i.e., when exact alignment is achieved), at which time, the optoelectronic components are xe2x80x9ctackedxe2x80x9d together in the aligned position by partially curing an adhesive at the interface (or joint) of the optoelectronic components. This partial curing is conventionally performed by irradiating the adhesive resin with UV radiation or with heat in the case of thermal cure adhesives such as epoxies.
Since the curing of thermal adhesives can cause movement of optoelectronic components relative to each other, alignment of optoelectronic components must be maintained during the curing process. Unfortunately, conventional adhesive resins may take a relatively long period of time to fully cure, which may increase the likelihood that misalignment will occur. In addition, UV-curable adhesive resins may absorb moisture that may cause deterioration of the adhesive and lead to loss of component alignment during subsequent use of the optoelectronic device. Also, conventional adhesive resin curing techniques may produce residual stresses in bonds between optoelectronic components that may cause undesirable creep and misalignment between adhesively joined optoelectronic components.
With the ever-increasing demand for optoelectronic components, there is a need for rapid, cost-effective methods of aligning and joining optoelectronic components for both in-situ and post curing processes. Furthermore, an adhesive curing method/technology that combines both in-situ and post curing is needed.
In view of the above discussion, both in-situ and post-cure methods of joining optoelectronic components such that they are optically coupled are provided. Methods according to the present invention may be utilized to join various types of optoelectronic components (e.g., optical fibers in adjacent end-to-end relationship, optical fibers to the active regions of various optoelectronic components, etc.)
An in-situ method of joining optoelectronic components according to an embodiment of the present invention includes positioning optoelectronic components in adjacent relationship such that light signals can pass therebetween, applying a curable resin having adhesive properties to an interface of the optoelectronic components, passing light signals between the optoelectronic components, aligning the optoelectronic components relative to each other such that the signal strength of light signals passing between the optoelectronic components is substantially maximized, and irradiating the interface with electromagnetic radiation to rapidly cure the resin such that the aligned optoelectronic components are fixedly joined. Irradiating the interface with electromagnetic radiation may include irradiating with non-ionizing radiation in the Radio Frequency (RF) and microwave regimes, according to embodiments of the present invention. Electromagnetic radiation can be applied using various applicators according to embodiments of the present invention, including fixed frequency, single mode microwave applicators, RF stray field applicators, capacitive heating applicators, and a variable frequency microwave (VFM) applicators. Moreover, microwave energy and RF energy can be used interchangeably.
Microwave applicators according to embodiments of the present invention may deliver single frequency RF and/or microwave energy, and may be configured to sweep with one or more ranges of RF and/or microwave frequencies selected to rapidly cure a resin, and may include the combination of single and variable frequency microwave energy, as well as a combination of RF and microwave energy.
A fixed frequency single mode microwave applicator, according to embodiments of the present invention, is equipped with an access port and door cut along a zero current, maximum field line. The access door enables access to the applicator cavity without disturbing the fundamental mode of heating. Furthermore, the terminations of a single mode applicator may be equipped with two plungers, one on each end, to increase the stability of the fundamental modes while enabling nano-positioning/alignment to take place. According to embodiments of the present invention, mode switching techniques can be used to target specific areas of a single mode applicator. Mode switching, according to embodiments of the present invention, can be performed through mechanical means (such as cavity dimensional changes) or through electronic means (such as changing incident frequencies).
The effective dimension of a single mode applicator can mechanically be changed through the use of plungers. A plunger is electrically connected with a cavity and is capable of linear travel to change the effective length of an applicator. The incident power can also be adjusted accordingly. Furthermore, microwave energy injected in a cavity at a given frequency or mechanical plunger set-up may be different from the energy injected inside the cavity at a different frequency or a different mechanical plunger set-up.
An RF stray field applicator, according to embodiments of the present invention, can be adjustable to various optoelectronic component assemblies. Electrodes of the RF stray field applicator can be dynamically adjusted during the cure process to localize and intensify the electric field at targeted positions/locations.
A capacitive heating applicator, according to embodiments of the present invention, utilizes capacitive plates that are interchangeable. The capacitive plates are adjustable to target different areas at different process times.
Methods and apparatus, according to embodiments of the present invention, are advantageous over conventional adhesive curing methods and apparatus for at least the following reasons: adhesives can be subjected to a controlled application of electromagnetic radiation, such as RF and/or microwave energy; the absorption of electromagnetic radiation within an optoelectronic component assembly can be controlled to selectively begin adhesive curing at predetermined areas; alignment of optoelectronic components can be controlled either simultaneously or sequentially with the application of electromagnetic radiation; alignment of optoelectronic components achieved during in-situ alignment can be maintained during post cure; and predetermined electromagnetic radiation process recipes can be utilized to optimize optical coupling for optoelectronic component assemblies that require post curing after in-situ UV curing.
Component alignment and electromagnetic radiation processing may occur substantially simultaneously according to embodiments of the present invention. According to other embodiments of the present invention, component alignment and electromagnetic radiation processing may occur sequentially. For example, alignment may occur to position the optoelectronic components in an optically coupled position, followed by electromagnetic radiation processing to partially cure the adhesive. Alignment techniques may be invoked again to verify that the optoelectronic components are still aligned or to reposition the optoelectronic components to an aligned position, followed by electromagnetic radiation processing to further cure the adhesive. This sequential pattern of aligning then applying electromagnetic radiation may be repeated numerous times until the optoelectronic components are permanently attached in the position that optimizes optical coupling.
According to embodiments of the present invention, portions of an optoelectronic component may be additionally heated via the use of susceptor material that is configured to heat to a predetermined temperature in the presence of electromagnetic radiation. Selective electromagnetic radiation causes susceptor material to heat to a predetermined temperature which, in turn, heats portions of an optoelectronic component to a predetermined temperature to facilitate curing of the adhesive resin. According to embodiments of the present invention, susceptor material may be added to portions of a positioning apparatus that holds/aligns optoelectronic components during electromagnetic radiation processing. For example, a gripping device may include one or more fluids (or other materials) in one or more portions thereof that is a susceptor material. A gripping device may also include susceptor material in a solid state.
According to embodiments of the present invention, fluid can be exchanged or drained from a gripping device to gain an additional degree of process control. For example, two fluid reservoirs may be utilized (e.g., one filled with a susceptor fluid such as a polar fluid, and one filled with a non-susceptor fluid, such as a non-polar fluid). Electromagnetic radiation can be applied while specific parts of the alignment set up can be made to heat or to cool during processing. Fluid heating or cooling during electromagnetic radiation exposure is not limited to the above described embodiments. Moreover, the term fluid is intended to include gases, liquids, slurries, etc.
A microwave absorbing gripper tool, according to embodiments of the present invention, may include internal polar fluid that is used to preheat an optoelectronic component assembly. The polar fluid may be drained to enable the microwave energy to focus on the optoelectronic assembly. A secondary fluid may be introduced to maintain temperature without interfering with the overall dielectric loading of the cavity. This may be especially beneficial in the case of single mode processing.
According to embodiments of the present invention, a secondary, non-polar fluid may be used for controlled cooling of an adhesive joint area. This can be achieved by introducing the non-polar fluid from a reservoir of known and controlled temperature. According to embodiments of the present invention, solid materials such as silicon carbide may be utilized as a microwave susceptor material.
A post-cure method of joining optoelectronic components according to an embodiment of the present invention includes positioning first and second optoelectronic components in adjacent relationship such that light signals can pass therebetween, applying a curable resin having adhesive properties to an interface of the optoelectronic components, passing light signals between the optoelectronic components, aligning the optoelectronic components relative to each other such that the signal strength of light signals passing between the optoelectronic components is substantially maximized, and irradiating the interface with electromagnetic radiation (e.g., RF and/or microwave energy) to partially cure the resin. The joined optoelectronic components are then transferred to a curing oven to fully cure the adhesive resin via either conventional techniques or via the application of electromagnetic radiation (e.g., RF and/or microwave energy).
According to embodiments of the present invention, a curing oven may be a conventional thermal oven, and the partially cured adhesive resin may be subjected to thermal heating at a predetermined temperature for a predetermined period of time. According to embodiments of the present invention, a curing oven may include a capacitive heating device, and the partially cured adhesive resin may be subjected to energy generated between a pair of parallel capacitive plates. According to embodiments of the present invention, a curing oven may include one or more RF stray field electrodes, and the partially cured adhesive resin may be subjected to a stray field of RF energy.
RF/microwave processing in accordance with embodiments of the present invention is advantageous over conventional thermal processing for numerous reasons. RF/microwave processing is rapid and selective. RF/microwave processing reduces the effects of viscous drag during curing which can lead to misalignment.
Good post cure results can be obtained when an optoelectronic component assembly is processed according to predefined curing xe2x80x9crecipesxe2x80x9d. For example, curing involving multistage heating and ramp rate adjusting between various heat soaking stages in variable frequency microwave (VFM) processing may minimize optoelectronic component movement compared with conventional convection curing techniques. Multistage heating may be tailored around the adhesive involved in the assembly process. Once the gel stage of the adhesive is identified, the VFM curing recipe is adjusted such that relaxation of the adhesive due to an increase in stresses is circumvented. In convection heating, achieving a given thermal stage is done slowly which may induce undesirable relaxations. These relaxations along with the thermal expansion that takes places in the materials forming the optoelectronic component assembly may result in the undesirable loss of alignment. VFM processes may lead to higher post cure process yields than convection heating because VFM facilitates rapid cure and selective heating of an optoelectronic component forming a given assembly.
According to embodiments of the present invention, electromagnetic radiation (e.g., RF and/or microwave energy) applicators are equipped with closed-loop feedback on temperature for proper process control. Measured temperature is computed to derive a heating rate. The heating rate is fed back to an electromagnetic radiation generator, which in turn delivers more or less electromagnetic radiation power, according to a programmed heat rate (recipe). Both contact and non-contact temperature monitoring systems may be used to measure temperature. Non-contact temperature monitoring systems, such as IR pyrometers, do not interfere with sensitive optoelectronic components to be aligned.
According to embodiments of the present invention, a microwave single mode applicator includes a housing that defines a microwave cavity. The housing has an access port formed therethrough through which optoelectronic components can be inserted into and removed from the cavity. The access port has a contour of a zero current line for the microwave cavity. An access door is movably mounted to the housing and is configured to be opened to permit access to the cavity via the access port. The housing also includes opposite first and second end portions with first and second plungers movably mounted within the first and second end portions respectively. Movement of the first and second plungers changes the physical dimensions of the cavity.
According to embodiments of the present invention, an optoelectronic component assembly system is provided that includes a microwave applicator having a housing that defines a cavity, a source of microwave energy configured to deliver microwave energy to the cavity, a positioning apparatus configured to align optoelectronic components in relation with each other within the cavity, an optical source configured to pass light signals between optoelectronic components being aligned by the positioning apparatus, and an optical detector configured to detect signal strength of light signals passing between the optoelectronic components. The microwave applicator housing has an access port formed therethrough through which optoelectronic components can be inserted into and removed from the cavity. The access port has a contour of a zero current line for the microwave cavity. An access door is movably mounted to the housing and is configured to be opened to permit access to the cavity via the access port. The housing also includes opposite first and second end portions with first and second plungers movably mounted within the first and second end portions respectively. Movement of one or both of the first and second plungers changes the physical dimensions of the cavity.
According to embodiments of the present invention, an RF stray field applicator is provided that includes an array of stray field electrodes configured to generate a stray field of RF energy, and wherein the electrodes in the array are movable relative to each other so that the electrodes can maintain a predetermined distance from a surface of a three-dimensional object to which a stray field of RF energy is to be applied. A distance between adjacent electrodes in the array may also be adjustable.
According to embodiments of the present invention, an optoelectronic component assembly system includes an RF stray field applicator, a positioning apparatus associated with the RF stray field applicator that is configured to align optoelectronic components in relation with each other, an optical source configured to pass light signals between optoelectronic components being aligned by the positioning apparatus, and an optical detector configured to detect signal strength of light signals passing between the optoelectronic components. The RF stray field applicator includes an array of stray field electrodes configured to generate a stray field of RF energy. The electrodes in the array are movable relative to each other so that the electrodes can maintain a predetermined distance from a surface of a three-dimensional optoelectronic component assembly to which a stray field of RF energy is to be applied. A distance between adjacent electrodes in the array may also be adjustable.